Fluid flow indicator with automatic alarm timer for low pressure/low flow applications

ABSTRACT

A highly sensitive low loss and low flow fluid flow switch is coupled with an automatic timer and/or optional transmitter to indicate the flow of gas to an appliance and to automatically start a reminder timer to turn the appliance off. After a preset time limit has expired, the timer either sounds an alarm or wirelessly triggers an alarm in a remote location. The receiver portion of the wireless timer may be mounted directly to the appliance (grill handle), so that the timer automatically resets when activity (cover opening or closing) is detected, indicating the appliance is still in use. An alarm can also be configured to sound when the grill is attempted to be ignited with the cover closed, thereby avoiding a potential explosion. A biasing attraction magnet is incorporated in the fluid flow switch to offset either the force of gravity or a return spring in order to extend performance to low pressure and low flow applications. The piston is sealed for use in high pressure/low flow applications, and provided with a vent hole for residual gas bleed-off upon a stoppage of gas flow.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application for a patent which is also disclosedin Provisional Application Ser. No. 61/009,725, filed on Dec. 29, 2007by the same inventor, namely David A. Struyk, and entitled “GAS FLOWINDICATOR WITH AUTOMATIC ALARM TIMER,” the benefit of the filing date ofwhich is hereby claimed.

BACKGROUND OF INVENTION

The present invention relates generally to the field of fluid flowindicators. More particularly, the present invention relates to a gasflow indicator which utilizes a highly sensitive gas flow switch incombination with a timer, alarm system and optional activity sensor foralerting the presence of sustained gas flow after a predetermined periodof time.

Gas-operated appliances, such as barbecue grills, deck heaters,fireplaces, and the like have become commonplace. The availability ofeither natural or propane gas as a fuel makes these appliancesparticularly convenient. However, it is commonplace for the users ofsuch appliances to accidentally leave the appliances turned on longafter their intended period of use. Portable propane tanks arefrequently exhausted after the users forget to turn the appliances off.This leads to an expensive waste of fuel, the inconvenience of refillingportable gas tanks, and a considerable safety hazard. The problem ismagnified when the appliances are plumbed directly to the availablenatural gas supply or household propane tank. With millions of gasgrills and other gas appliances being sold around the world each year,clearly an effective signaling/safety device is desirable.

Others have heretofore attempted to solve the above problem. Nearly allsuch attempts, however, have resulted in devices in which the intendedpurpose is to turn off the appliance (cease gas flow) after a certainpredetermined amount of time. Patents disclosing this type of a gas flowcontrol device include the following: U.S. Pat. Nos. 6,684,757;5,628,242; 4,823,838; 6,733,276; 5,813,394; 6,289,792; 5,617,840;7,117,893; and 5,333,596. To the knowledge of the applicant, however,none of these devices have ever become standard equipment on anycommercially available gas appliance.

The reason for this is due primarily to the increased liabilityassociated with such devices. Once a device of this nature is installed,there becomes an assumption of safety on the part of the owner, wherehe/she begins to rely on such a device as a convenience feature designedto automatically turn off the appliance. While it may indeed beconvenient, should the device fail for any reason, the device which wasoriginally intended as a safety feature, is now regarded as the cause ofsomething potentially catastrophic.

In such devices, a single “upstream” valve is virtually always disclosedas a master valve to cut off the supply of gas to the burners. However,the individual burner valves will still remain in their previously openposition, allowing even small amounts of gas to pass in the event themaster cutoff valve fails to seal completely. This accumulated gas couldlead to a catastrophic explosion the next time the appliance isoperated. Therefore, gas-operated appliance manufacturers have beenreluctant to include such “automatic” devices on their products,preferring instead to rely on the user to turn off the device himself,effectively leaving responsibility, and therefore liability, with theuser.

In U.S. Pat. No. 5,608,383, an automatic temperature alarm system isdisclosed, wherein the device is more appropriately intended to be awarning device rather than a shut-off switch. This device utilizes atemperature sensor to detect operation of a gas grill and a vibrationsensor to detect whether the grill has been untouched for an excessiveperiod of time, thereby sounding the alarm. Any detection of vibrationcauses a timer to reset, thus preventing the alarm from sounding.

Regardless of the type of system utilized, reliable detection ofappliance operation is paramount. Unfortunately, with today's moresophisticated gas appliances, temperature is not the best means fordetecting operation. In older gas grills, for instance, where there mayhave been only one or two burners, both housed within a single grillchamber, a single temperature sensor may have been sufficient. But withtoday's grills, multiple burners, as well as accessory side burners anddedicated rotisserie burners, are common. This would require multipletemperature sensors to accurately determine whether or not the grill isactually operating, complicating installation and raising the cost ofimplementation.

Other detection mechanisms have also been previously contemplated. Thedetection of gas valve/knob position would only indicate an intent touse, and all valves/knobs would need to be individually instrumented.Flame detection and non-contact infra-red suffer from the samemulti-burner issues as the temperature sensor. External non-contactinfrared also suffers from issues of “field of view”, sensorcontamination, and varying surface properties. Additionally, calibrationis required for the property known as emissivity, making the same systemdifficult to use on appliances constructed of different outer materials,such as porcelain enamel versus stainless steel.

A more viable and safer alternative for detecting operation of a gasappliance is to sense gas flow to the appliance. Detecting gas flow hasthe advantage in that it can reliably cover all burners, whether ignitedor not, from a single location. However, sensing the flow of gas in agas grill is complicated by the fact that both the pressure and the flowrate of gas to the grill are extremely low. For instance, in a typicalpropane gas grill, high pressure liquefied propane is stored in aportable tank attached to the grill. The pressure in the tank varieswith temperature, but may well be over 150 psi. Because of this, a lowpressure regulator is required to reduce the pressure of the gas to asafe working pressure of just 11″ water column (WC), which is just 0.4psi. For natural gas systems, the pressure is even lower, typically just7″ WC, or 0.25 psi. In the case of propane, the rate of flow on the highpressure side of the regulator, due to the increased pressure, is evenlower than that on the low pressure side. This makes reliable detectionof the flow of gas difficult.

Gas flow switches/detectors are available in the prior art, but most areill-suited for use in low pressure/low flow applications. They areavailable in many forms, but typically employ a piston or a vane, whichactivates an electrical switch. Piston designs can be used in what isknown as “positive displacement” configurations. While a typical gasflow switch may indicate when the flow rate is above a particularthreshold, a positive displacement design ideally does not allow gas toflow at all without providing an indication.

In such a device, a differential pressure generated within the switchbody between the input and the output provides the necessary operatingforce to move the piston out of the way, allowing gas to flow.Typically, a magnet residing within the piston is used to trigger anexternal reed switch or Hall effect sensor attached to the flow switchbody, thereby detecting the flow of gas. A spring, magnet, or gravity isgenerally used to provide the return force necessary to reset the gasflow switch in the absence of gas flow.

U.S. Pat. No. 6,684,757 mentions in passing the possibility of detectingoperation of a gas grill via the detection of gas flow, but it fails toaddress the problem and difficulty of sensing gas flow in such a lowpressure/low flow application as is present with the gas grillappliance. For such low pressure applications, where the gas flow switchmay be placed downstream of the pressure regulator, both the flow andthe pressure are too low for a typical flow switch. Such switches tendto reduce pressure and restrict flow, thus hindering the performance ofthe appliance. Furthermore, whether positioned downstream or upstreamfrom the pressure regulator, pistons utilized in such gas flow switchesare commonly subject to oscillation. Therefore, enhancements must bemade in order for reliable gas flow detection to function withoutsignificant pressure loss and flow restriction.

It is therefore an object of the present invention to provide a novelconfiguration of a fluid flow indicator/switch which is highly sensitiveand useful for detecting the flow of gas in low flow applications, suchas with gas grills and the like, and which will function accuratelywithout significant pressure loss or flow restriction.

It is also an object of the present invention to provide a novelconfiguration of a piston-type positive displacement fluid flowindicator/switch which is highly sensitive and useful for detecting theflow of gas in low flow applications, such as with gas grills and thelike, and which is devoid of any substantial piston oscillation.

It is still a further object of the present invention to provide such anovel and useful fluid flow indicator which utilizes a highly sensitivefluid flow switch in combination with a timer, alarm system and optionalactivity sensor for alerting the presence of sustained gas flow after apredetermined period of time.

BRIEF SUMMARY OF THE INVENTION

It will be noted that the present invention pertains primarily to theuse of gas-operated appliances, such as gas grills, gas patio heaters,gas fireplaces, and the like. Although it is contemplated that thepresent invention would also be useful in applications involving thedetection of liquid flow rates, it is deemed to have particularsignificance in connection with the detection of extremely low rates ofgas flow in gas-operated appliances. For this reason, the discussionherein will focus primarily on fluid flow indicators for gas-operatedappliances, it being understood that the principles of my inventionapply equally to applications involving the flow of a liquid. Forfurther ease of illustration, the discussion hereafter will also belimited primarily to the context of a gas grill, it being understoodthat the principles of the present invention apply equally to all gasappliances.

It is the goal of this invention to provide an inexpensive, convenientto use, and easily installed low loss/low flow gas flow switch whichprovides a warning signal after a predetermined time of operation of agas grill. In this way, the user will be reminded to turn off the gasgrill after such time has expired. In the present invention, detectionof gas flow is used to automatically set a timer, which may or may notinclude an activity sensor to reset the timer, and either a local alarm,a wirelessly linked alarm, or both. The gas flow switch of the presentinvention is of an inline, coaxial design, incorporating a lightweightpiston that travels in a close fitting cylinder. It incorporates a reedswitch which is activated via a magnet carried in the piston uponsensing the flow of gas. Activation of the reed switch in turn initiatesan alarm timing mechanism that is set for a predetermined acceptabletime of operation.

The gas flow switch may be installed either upstream or downstream ofthe gas flow regulator. If downstream of the regulator, where both thepressure and flow of gas is extremely low, the gas flow switch isintended to be installed in a vertical orientation. In normal operation,when the flow of gas is turned on by one of the grill burner valves, asmall differential pressure provides a sufficient lifting force to raisethe piston above the outlet ports, allowing gas to flow to the grill,and simultaneously activating the reed switch.

Even the lightest weight piston, however, will decrease the availablegas pressure to the grill, causing performance of the grill to suffer.Therefore, in order to effectively reduce the weight of the piston, apiston biasing member in the form of a second attractive biasing magnetis positioned at the upper end of the cylinder to attract the piston,thereby reducing the pressure necessary to support it above the outletports. This biasing magnet acts as a non-linear spring, providing anincreasing force of attraction as the piston gets closer, actinginversely to any mechanical spring. The biasing magnet is sizedappropriately so that it is not capable of supporting the weight of thepiston without the addition of some differential pressure. Therefore,when the gas flow is turned off, the differential pressure equalizes,and the piston returns to its “OFF” or resting position by the force ofgravity.

In the case of installation on the high pressure side of the regulator,the flow switch is generally installed in a horizontal orientation, andmay be fitted with ACME/QCC-1 (CGA791) input and output couplingconnections for quick and easy installation between the propane tank andlow pressure regulator. With this configuration, gravity will not workto return the piston to its gas “OFF” or resting position; therefore, aspring is used to generate the required return force. In this case, thespring may be used in combination with the attractive biasing magnet toreduce the pressure necessary to activate the reed switch, as thebiasing magnet has the effect of linearizing and reducing the force ofthe return spring. Since gas flow is extremely low on this side, inorder to prevent gas “blow-by,” the piston is sealed relative to thepiston cylinder. A piston vent hole is then provided to allow for theescape of gas upon return of the piston to its resting position. Thespring and vent hole are appropriately sized to ensure both pistontravel at the lowest possible flow rate, and the reliable return of thepiston to its gas OFF position when the flow ceases.

Piston oscillation is also a significant problem with such gas flowswitches, particularly downstream of the pressure regulator, where gaspressure is low. The biasing magnet, along with a semi-sealing magnetsupport positioned at the end of the internal cylinder which houses thepiston, dampens piston oscillation by way of providing stabilizingforces. The coaxial nature of the inner cylinder concentric within theprimary outer chamber, allows for a semi-sealed chamber beyond thepiston, thereby forming a dashpot damper. This, in conjunction with theattractive magnet, completely eliminates oscillation of the piston.

These improvements effectively create a highly sensitive low loss/lowflow gas flow switch which may be coupled with an automatic timer and/oroptional transmitter to indicate the flow of gas to an appliance and toautomatically start a reminder timer to turn the appliance off. After apreset time limit has expired, the timer either sounds an alarm orwirelessly triggers an alarm in a remote location. The receiver portionof the wireless timer may be mounted directly to the appliance (grillhandle), so that the timer automatically resets when activity (coveropening or closing) is detected, indicating the appliance is still inuse. An alarm can also be configured to sound when the grill isattempted to be ignited with the cover closed, thereby avoiding apotential explosion.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will more fullyappear from the following description, made in connection with theaccompanying drawings, wherein like reference characters refer to thesame or similar parts throughout the several views, and in which:

FIG. 1 is a perspective view of a gas flow switch embodying theprinciples of the present invention and configured for use in lowpressure/low flow applications;

FIG. 2 is a perspective sectional view of the gas flow switch in FIG. 1,with a cutaway section thereof removed to illustrate the configurationand operation of the switch under no gas flow conditions;

FIG. 3 is a vertical sectional view of the gas flow switch in FIG. 1,also illustrating the configuration and operation of the switch under nogas flow conditions;

FIG. 4 is a perspective sectional view of the gas flow switch in FIG. 1,with a cutaway section thereof removed to illustrate the configurationand operation of the switch when gas is flowing;

FIG. 5 is a vertical sectional view of the gas flow switch in FIG. 1,also illustrating the configuration and operation of the switch when gasis flowing;

FIG. 6 is a perspective view of an alternative embodiment of a gas flowswitch embodying the principles of the present invention and configuredfor use in high pressure/low flow applications;

FIG. 7 is a perspective sectional view of the gas flow switch in FIG. 6,with a cutaway section thereof removed to illustrate the configurationand operation of the switch under no gas flow conditions;

FIG. 8 is a vertical sectional view of the gas flow switch as shown inFIG. 6, also illustrating the configuration and operation of the switchunder no gas flow conditions;

FIG. 9 is a perspective sectional view of the gas flow switch in FIG. 6,with a cutaway section thereof removed to illustrate the configurationand operation of the switch when gas is flowing; and

FIG. 10 is a vertical sectional view of the gas flow switch in FIG. 6,also illustrating the configuration and operation of the switch when gasis flowing.

FIGS. 11A, 11B and 11C depict an integrated flow chart systemillustrating the operation of an alarm timing mechanism whichincorporates a gas flow switch embodying the principles of my invention.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIGS. 1 thru 5 is a fluid/gas flow switch 1 constructed inaccordance with the present invention and configured for installationand use downstream of a typical gas grill appliance pressure regulator,or for use with household natural gas, where both the pressure and flowof gas is extremely low. The gas flow switch 1 includes an outer housing3 with a threaded gas inlet port 5 and threaded outlet port 7. Gas flowswitch 1 is therefore adapted to be threadably and sealably connected invertical orientation (with inlet port 5 below the outlet port 7) inlinewith the gas line leading to the gas grill, downstream of the pressureregulator.

As shown in FIGS. 2 thru 5, the outer housing 3 includes an interiorbore or chamber extending therethrough within which inner cylinder 9 isseated in sealed relation via o-ring 11. Inner cylinder 9 in turncarries piston 13 within its confines in close, free-floating slip-fitrelation. Adjacent the inlet end of the flow switch 1, the housing 3forms a radially inwardly protruding shoulder stop 15 for inner cylinder9 and piston 13. Inner cylinder 9 is held firmly in place within housing3 by cylinder head 17 and retaining ring 19 located adjacent the outletend of flow switch 1.

In the low pressure/low flow embodiment shown in FIGS. 1 thru 5, piston13 is uniquely designed to carry two (2) thin Neodymiumswitch-activating magnets, 21 and 23, rather than a single magnet.Magnets 21 and 23 are inserted from opposite ends of the piston 13, andheld in place by mutual attraction, separated only by a small inwardlyprotruding shoulder or rib 25. This design allows for the magnets 21 and23 to “float” slightly within a very lightweight piston 13, thusaccommodating changes in temperature, and avoiding the use of messyadhesives. Recessing the magnets 21 and 23 within the piston 13 alsoenables them to capture by magnetic attraction small foreign metallicmatter entering cylinder 9, thus preventing potential lodgment of suchmatter between the walls of piston 13 and cylinder 9, and consequentadverse operation of the grill.

The inner cylinder 9 includes a plurality of fluid flow orifices or gasoutlet ports 29 extending through its outer wall, which communicatefreely with a gas flow pathway 31 formed between the reduced outerdiametrical surface 33 of inner cylinder 9 and the inner chamber surface35 of housing 3. As shown best in FIGS. 2 and 4, pathway 31 thencommunicates with outlet port 7 of the gas flow switch 1 through aplurality of peripheral openings 37 formed in cylinder head 17 to allowgas to pass therethrough.

The gas flow switch 1 incorporates a reed switch 39 (or Hall effectsensor) which is activated via switch-activating magnets 21 and 23carried in the piston 13 upon sensing the flow of gas. As shown in FIGS.2 thru 5, in the preferred embodiment, reed switch 39 is collocated on atransmitter printed circuit board 41 (PCB), which is attached to theouter housing 3 of the gas flow switch 1. The electronics, comprisingthe transmitter PCB 41, battery 43 and a small loop antenna 45, arelocated under a plastic cover 47 affixed the housing 3 of gas flowswitch 1.

As will be discussed in more detail hereafter, activation of the reedswitch 39 in turn initiates an alarm timing mechanism (not shown) thatis set for a predetermined acceptable time of operation. It is deemeddesirable that the actual transmitter circuit never needs batteryreplacement; therefore, it has been designed with a single smalllifetime battery 43. Battery 43 is expected to last up to 20 years, withnormal usage, never requiring a change. Therefore, the entiretransmitter electronics package may be potted, or filled with an epoxylike sealant, allowing for all weather operation.

In FIGS. 2 and 3, the gas flow switch 1 is shown in a gas “OFF”position, with piston 13 resting against shoulder stop 15 at the inputend of cylinder 9. In this position, the magnets 21 and 23 within thepiston 13 are sufficiently far from the reed switch 39 so that it is notactivated. As shown in FIGS. 4 and 5, when the flow of gas is turned“ON” by one of the grill burner valves, a small differential pressureprovides a sufficient lifting force to raise the piston 13 above theoutlet ports 29, allowing gas to flow through outlet ports 29, intopathway 31 and out through port 7 to the grill. Simultaneously, reedswitch 39 is activated, thus triggering detection of the flow of gas andactivating the alarm timing mechanism.

However, even the lightest weight piston 13 will decrease the availablegas pressure to the grill, causing performance of the grill to suffer.In order to effectively reduce the weight of the piston 13 and counterthe force of gravity, an attractive biasing member or magnet 49 isembedded in the cylinder head 17 positioned at the upper end of thecylinder 9. This biasing magnet 49 attracts magnets 21 and 23 carriedwithin the piston 13, thereby helping to attract piston 13 toward itsswitch-activating position and effectively reduce the pressure necessaryto support it above the outlet ports 29.

The attractive biasing magnet 49 acts as a non-linear spring, providingan increasing force of attraction as the piston gets closer, actinginversely to any mechanical spring. This is an ideal solution toreducing the effective weight of piston 13, as it only acts on thepiston 13 after it has been raised, allowing it to fully return to itsrest position. The biasing magnet 49 is sized appropriately so that itis not capable of supporting the weight of the piston 13 without theaddition of some differential pressure. Therefore, when the gas flow isturned off, the differential pressure equalizes, and the piston 13returns to its “OFF” or resting position by the force of gravity.Achieving this effect mechanically would introduce friction andhysteresis, negatively affecting the performance of the sensor. Thisapproach provides a nearly frictionless lifting force, as the piston canfreely fall with very little drag from the cylinder sidewalls.

FIGS. 6 thru 10 of the drawings illustrate an alternative embodiment ofa gas flow switch 101 which is designed for connection between a typicalgas grill propane tank and the existing low pressure regulator, wheregas pressure is high but the rate of gas flow is even lower. In thisembodiment, the integrated gas flow switch is fitted with an ACME/QCC-1(CGA791) female input connector 103 and a similar male output connector105 for quick and easy installation by the grill owner. In the preferredembodiment, it is contemplated that the connector 103 will be connecteddirectly to the propane tank. Therefore, in this embodiment, flow switch101 will likely be horizontally oriented, versus the verticalinstallation of gas flow switch 1 on the low pressure side of thepressure regulator.

As seen best in FIGS. 7 thru 10, the main housing body 107 of gas flowswitch 101 and the tank connector 103 are cooperatively threaded tofacilitate a sealed threadable engagement therebetween. The opposite oroutlet end of housing 107 is integrally formed as a male QCC-1 coupler105 with a typical internal safety gas valve 109 contained therewithin,similar to that of a standard propane tank. With the ability to connectthe gas flow switch 101 directly inline to a standard propane tank, itis evident that this configuration is particularly well-suited for useas an aftermarket add-on product.

The gas flow switch 101 is generally constructed and functions in amanner similar to gas flow switch 1 of the previous embodiment. As shownin FIGS. 7 thru 10, gas flow switch 101 similarly includes an innercylinder 111, piston 113 with switch-activation magnets 115 and 117, andan electronic module comprising a reed switch (or Hall effect sensor)119, transmitter PCB 121, battery 123 and antenna 125 contained by cover127.

However, detection of the flow of gas on the high pressure side of theregulator presents an additional problem. The flow of gas is so lowthat, unless the piston is sealed against the piston cylinder wall, thegas will leak around the piston without any appreciable force beingapplied thereto. Therefore, in order to prevent such gas blow-by, thepiston 113 is configured to carry an outer annular seal 143 which sealsthe piston 113 against the wall of the inner cylinder 111, yet allowsthe piston 113 to move readily between its “OFF” resting position (FIGS.7 and 8) and its switch-activating position (FIGS. 9 and 10).

In the absence of gas flowing, piston 113 must return to its restingposition. In order for this to occur, any residual gas contained in theforward end 145 of cylinder 111 must be allowed to slowly escape.However, since piston 113 is sealed relative to cylinder 111, suchresidual gas cannot dissipate around the piston and will thus restrictthe return of piston 113 unless some means of escape is provided. Toaccomplish this, piston 113 is provided with a vent hole 147 whichextends axially through the middle thereof, thus allowing any residualgas in the forward end 145 of cylinder 111 to seep through to the otherside of piston 113 upon a stoppage of gas flow. While tolerancerequirements between piston 113 and cylinder 111 make it difficult toprevent gas blow-by without seal 143, it has been found that the use ofsuch a sealed piston configuration 113 with a vent hole 147 canadequately provide the desired response characteristics for thedetection of gas flow on the high pressure side of the regulator.

Since gas flow switch 101 is configured for installation in thehorizontal position, gravity will not aid in returning the piston 113 toits original resting or gas “OFF” position upon a stoppage of gas flow.Therefore, a very weak spring 129 is carried within cylinder 111 andused to provide force against piston 113 for the return to its restingposition at the inlet end of cylinder 111 when the flow of gas is cutoff. The spring and vent are adjusted in combination to ensure pistontravel at the lowest possible gas flow, i.e. that of a single burner atits lowest setting, while still allowing for the piston to fully returnto its gas off position in the absence of gas flow. The spring needs tobe strong enough to overcome the additional friction of the seal, whilethe hole needs to be small enough to allow sufficient gas pressure tobuild within the cylinder to move the piston, thereby activating thereed switch at the lowest possible flow rate without bypassing throughthe vent itself. In this case, a biasing magnet 149, similar to thebiasing magnet 49 utilized in gas flow switch 1 of the previousembodiment, can be used to offset and linearize the force of the spring,thus reducing the differential pressure necessary to activate theswitch. This is beneficial, as at higher pressures the flow rate issignificantly reduced, making it difficult to generate sufficientpressure to overcome the spring force and activate the switch.

To accommodate spring 129, piston 113 is constructed such that piston113 defines a chamber 131 facing cylinder head 133 and the outlet of gasflow switch 101. As shown, spring 129 seats within chamber 131 and isretained thereby. The opposite end of spring 129 seats against biasingmagnet 149 within the cylinder head 133 covering the outlet of innercylinder 111, which is retained by retaining spring 135.

In a similar manner to the previous embodiment, in FIGS. 7 and 8, thegas flow switch 101 is shown in a gas “OFF” position, with piston 113being held in place by spring 129 against shoulder stop 137 at the inputend of cylinder 111. In this position, the magnets 115 and 117 withinthe piston 113 are sufficiently far from the reed switch 119 so that itis not activated. As shown in FIGS. 9 and 10, however, when the flow ofgas is turned “ON” by one of the grill burner valves, a smalldifferential pressure provides a sufficient force to move the sealedpiston 113 past the outlet ports 139, allowing gas to flow into pathway141, through safety valve 109 and out of the gas flow switch 101 to thegrill. Simultaneously, reed switch 119 is activated, thus triggeringdetection of the flow of gas and activating the alarm timing mechanism.

When the gas flow is turned off, the differential pressure equalizes,and spring 129 exerts a force against piston 113 to return it to its“OFF” or resting position. Any residual gas retained in the forward end145 of the piston cylinder 111 will bleed off and escape through venthole 147 in piston 113, thus allowing piston 113 to return to itsresting position.

In either embodiment, the gas flow switch (1, 101) is designed tofunction in applications involving extremely low rates of gas flow, andis therefore quite sensitive to any change in gas pressure. Under suchcircumstances, and particularly in low pressure/low flow applications,conventional gas flow switches commonly experience piston oscillationcaused by sudden variances in gas pressure. In the present invention,however, each embodiment of the gas flow switch (1, 101) is designedwith a dashpot dampening mechanism to alleviate any such pistonoscillation.

In both embodiments, the attractive biasing magnet (49,149), along withthe semi-sealing cylinder head (17,133) at the end of the internalcylinder (9,111) helps to dampen piston oscillations by way of providingstabilizing forces. The coaxial nature of the inner cylinder (9,111)concentric within the primary outer chamber of the housing (3,107)allows for a semi-sealed chamber (51,131) (see, FIG. 3, 8) beyond thepiston (13,113) forming a dashpot damper. This, in conjunction with theattractive magnet (49,149), completely eliminates oscillations of thepiston (13,113).

As noted previously, in either embodiment, integrated with the gas flowswitch (1, 101) is an alarm timing mechanism. This alarm timingmechanism may incorporate an automatic alarm timer and alarm, or in thepreferred embodiment, a wireless transmitter for remote activationthereof. In both configurations, the gas flow switch, circuit board,power supply, and housings are all integrated. This provides for easyinstallation. In the high pressure approach, the integrated flow switch101 is fitted with ACME/QCC-1 (CGA791) input and output connections 103and 105 for quick and easy installation by the grill owner between atypical gas grill propane tank and the existing low pressure regulator.For factory installed applications (Original EquipmentManufacturer—OEM), or for use with household natural gas, connection tothe low pressure side using gas flow switch 1 is preferred. Theintegrated housing of flow switch 1 is quite small, allowing directinline installation in the gas line using standard tapered or flarefitting connections.

With reference to the flow charts shown in FIGS. 11A, 11B and 11C,operation of the integrated alarm timing mechanism can be illustratedand explained. As denoted at step 151 in FIG. 11A, when gas flows, theflow switch (1, 101) turns on and the switch-activating magnets (21, 23;115, 117) actuate the reed switch (39, 119), thereby activating thetransmitter PCB (41, 121). The circuit is completely off before thispoint, conserving battery power. The status of the battery (43, 123) iscombined with the “GAS-ON” indication and transmitted to the receiver(step 153). The transmitter then enters a power saving sleep mode andwaits for the gas flow to stop. When this occurs, the status of thebattery (43, 123) is again combined with the GAS-OFF indication andtransmitted to the receiver (step 155). The transmitter circuit thenpowers down.

In the preferred embodiment, when the flow of gas is detected, thetransmitter wirelessly sends a “GAS-ON” signal to the receiver of thealarm timing mechanism, which may be mounted on the grill itself, atsome other remote location, or both. As seen in FIG. 11B, the receivercircuit, after a power-on reset, runs in a continuous loop 159 thatconstantly listens for a valid received signal. Upon reception, itdetermines whether it was a GAS-ON or a GAS-OFF signal. If GAS-ON, itsets the ON-FLAG, which is used to start the timer, sounds the ON beepand LED, and sets the initial time to around 90 minutes (step 161). Ofcourse, this time may be adjusted as desired or needed. If it receives avalid GAS-OFF signal, it resets the ON-FLAG, sounds the OFF beep andturns off the LED; it also resets the alarm in case it was previously on(step 163). With each reception, the transmitter battery is checked andthe status displayed with an additional LED.

Once the ON-FLAG is set (step 165), with each pass through the loop 159,accessory buttons 167 (i.e., rotisserie) and an optional activity sensor169 are checked. If the rotisserie button is pressed, the receiver/timerenters a ROTISSERIE mode, where a rotisserie LED is lit and the timer isset to a much longer time, such as 4 hours (step 171). If the rotisseriebutton is subsequently pressed, the ROTISSERIE FLAG 173 providestoggling between modes; when deactivated, the ROTISSERIE LED is turnedoff, and the timer returns to the usual 90 minute setting.

If the optional activity sensor is used, this automatically resets theremaining time to shorter intervals, i.e., 30 minutes for the normalmode, and 120 for the rotisserie mode (step 175), and the countdownbegins again. If the alarm has been activated, then pressing the resetbutton manually resets the alarm timer to 30 or 120 minutes depending onthe mode. If the receiver is mounted on the grill handle, user activitycan be detected in the form of a tilt switch which senses the cover hasbeen opened or closed. Certain conventional grills already employ suchgrill handle activity sensors to turn on a cooking light, and couldeasily be adapted to incorporate such a receiver. A remotely placedreceiver, such as in a residential kitchen, does not employ an activitysensor and simply begins counting down after the “GAS-ON” signal isreceived. In this case, the handle mounted receiver can optionallycontain an additional transmitter to signal other remote receivers ofgrill activity so that they can also reset their timers.

As shown in FIG. 11C, the alarm timer routine 167 runs independently ofthe receiver routine and activates the alarm after the time hasdecremented to zero. The ON FLAG 169 prevents the alarm from beingactivated when the grill is off. When the ALARM FLAG is set by the alarmtimer, the hardware sounds the alarm.

If the grill, and thus the gas, should be shut off before the time hasexpired, the transmitter sends a “GAS-OFF” signal to the receiver(s),prompting the receiver's timer unit to reset itself, as at step 163, andwait for the next GAS-ON signal. If a receiver timer should reach itslimit, it is assumed that the operating grill has been forgotten, and areminder alarm is sounded. The receivers are fitted with a push buttonto disable the alarm, and reset the timer to another predetermined time,30 minutes for example. If the receiver still has not received a GAS-OFFsignal after this new period of time, the grill alarm sounds again. Thiswill happen indefinitely until the grill is turned off.

Each receiver is powered by easily replaceable AA type batteries, orconfigured with a typical AC plug. The operating range of thetransmitter/receiver combination is approximately 100 feet. As notedpreviously, included with each and every transmission, is the batterystatus. In the unlikely event the grill should ever out last thetransmitter battery (43, 123), a low battery status alarm will beactivated in the receiver/alarm, indicating it is time to replace thetransmitter unit. Since the receiver/timer units need to always be“listening” for a GAS-ON signal, they consume more power than thetransmitters, and have therefore been designed with easily replaceablebatteries or a direct AC power connection.

When used with the activity sensor, to avoid a possible explosion, ifthe flow of gas is first detected while the grill cover is closed, thesystem will sound the alarm until either the flow of gas is turned offor the cover is opened. This is not possible with other means ofoperation detection, such as temperature or flame detection, where theresponse is too late. This feature can also be integrated with the grillignition system to actually prevent the ignition spark from occurringwhile the cover is closed, rather than just sounding an alarm.

Obviously, in such case, it is highly desirable for the flow switch (1,101) to have a fast response when alerting the user that the cover isclosed while attempting to ignite the grill. Therefore, it iscontemplated that the dashpot performance of the gas flow switch may beeasily adjusted to improve switch performance by incorporating a smallvent hole or grooves (not shown) in the respective cylinder head (17,133) of the flow switch (1, 101), so that a minimum of damping occurs,thus allowing for a faster response.

The gas flow switch (1, 101) of either embodiment is fabricated from gassafe components. The outer housing (3, 107) is preferably fabricatedfrom brass, and the electronics module cover (47, 127) of plastic. Thepiston (13, 113) and inner cylinder (9, 111), on the other hand, areideally constructed of aluminum. This ensures that the piston will be aslight weight as possible, and that sizing tolerances between the pistonand inner cylinder will remain consistent during thermal expansion andcontraction. Thus, even though the piston and cylinder are closefitting, operation across the temperature of interest will not beaffected.

In the preferred embodiment, the gas flow switch (1, 101) is completewith a small wireless transmitter and power supply. The transmitter isideally in the 433 MHz region, where operation is allowed by the FCC andfrequencies are low enough to pass through walls of ordinaryconstruction, necessary if the transmitter is located out of doors withthe grill, and the receiver is perhaps located indoors. The 915 MHzregion could also be considered. It would provide for smaller antennas,but the indoor/outdoor transmission may suffer.

It is possible that modern grill configurations could potentially causetransmission problems. The lower pedestal of a modern gas grill isfrequently configured as a cabinet, providing a location to “hide” thepropane tank and keep it from view. These are typically constructed ofmetal, and can be problematic for the transmitter if located at the tankas in the high pressure application, or connected near the manifold asin the low pressure application. The metal cabinet forms a shield,effectively blocking radio transmissions from the transmitter antenna tothe receiver.

To overcome this, rather than use a typical antenna, connection can bemade directly to the brass housing (3,107) of the gas flow switch(1,101). Thus, when connected to the propane tank, as in the highpressure application, the tank becomes a highly effective antenna,coupling to other metal structure that it is in contact with, andradiating beyond the cabinet. In the low pressure application, whenconnected to the metal gas line near the valves and manifold, the entireupper structure of the grill becomes the radiating element. In eachcase, the problem of the closed cabinet is eliminated.

When the above items are combined, the present invention provides a safeand effective means to prevent accidental gas appliance operation in theevent the operator forgets to turn the appliance off. It is highlyeffective, simple and easy to install, but still leaves the ultimateresponsibility of turning off the appliance with the operator.

It will, of course, be understood that various changes may be made inthe form, details, arrangement and proportions of the parts withoutdeparting from the scope of the invention which comprises the mattershown and described herein and set forth in the appended claims.

1. A fluid flow switch for detecting exceptionally low rates of fluidflow, comprising: (a) a housing having an inlet port, an outlet port andan interior piston chamber extending between and communicating with saidinlet port and said outlet port; (b) a gravity-induced piston carriedwithin said piston chamber, said piston being movable from a restingposition to a switch-activating position in response to the presence offluid flowing through said piston chamber, and being returned to saidresting position under the force of gravity in the absence of fluidflowing through said piston chamber; (c) a switch operatively disposedfor activation upon movement of said piston to said switch-activatingposition; and (d) a piston biasing member carried by said housing andbeing adapted to draw said piston against the force of gravity towardsaid switch-activating position.
 2. The fluid flow switch of claim 1,wherein said piston biasing member is comprised of a magnet.
 3. Thefluid flow switch of claim 1, wherein said piston biasing member isadapted to exert an increasing attractive force on said piston as saidpiston is drawn closer thereto.
 4. The fluid flow switch of claim 3,wherein the maximum attractive force exerted on said piston by saidpiston biasing member is less than the force of gravity on said piston,such that in the absence of fluid flowing through said piston chamber,the weight of said piston will overcome said attractive force and returnsaid piston to said resting position.
 5. The fluid flow switch of claim1, wherein said switch is an electrical switch that is magneticallyactivated by a switch-activating magnet carried by said piston when saidpiston is located in said switch-activating position.
 6. The fluid flowswitch of claim 5, including a power source, a transmitter and areceiver for activating an alarm, whereupon activation of saidelectrical switch electrically connects said power source to saidtransmitter, thereby causing a wireless electronic signal to betransmitted to said receiver to activate said alarm.
 7. The fluid flowswitch of claim 6, wherein said electrical switch, said power source andsaid transmitter are integrated as a single unit with said housing. 8.The fluid flow switch of claim 6, wherein said transmitter includes anantenna electrically connected to an outer metallic body portion of agas-operated appliance with which said fluid flow switch is used,thereby converting said gas-operated appliance into an extension of saidantenna.
 9. The fluid flow switch of claim 1, wherein said piston isconstructed to carry a pair of free-floating switch-activating magnets,said switch-activating magnets being disposed on opposite sides of ashoulder member and held in place through mutual magnetic attraction.10. The fluid flow switch of claim 1, wherein said piston chamber iscomprised of a piston cylinder within which said piston is carried, saidpiston cylinder having a cylinder wall with a fluid-flow orificeextending therethrough, and opposite ends adjacent said inlet and saidoutlet ports, said piston cylinder being capped at said end adjacentsaid outlet port, thereby forming a dashpot damper to minimizeoscillation of said piston.
 11. The fluid flow switch of claim 10,wherein said capped end of said piston cylinder carries said pistonbiasing member.
 12. The fluid flow switch of claim 1, wherein saidpiston forms a recess adjacent said inlet port of said housing for thecapture of debris particles contained within the fluid through themagnetic attraction of a switch-activating magnet carried by saidpiston.
 13. A fluid flow switch and alarm apparatus for detectingexceptionally low rates of fluid flow and producing an alarm warning,comprising: (a) a housing having an inlet port, an outlet port and aninterior piston chamber extending between and communicating with saidinlet port and said outlet port; (b) a piston carried within said pistonchamber, said piston being movable from a resting position to anelevated switch-activating position in response to the presence of fluidflowing through said piston chamber, and being returned to said restingposition under the force of gravity in the absence of fluid flowingthrough said piston chamber; (c) a piston biasing magnet carried by saidhousing and being adapted to magnetically draw said piston against theforce of gravity toward said switch-activating position; (d) anelectrical switch adapted to be magnetically activated by aswitch-activating magnet carried by said piston when said piston islocated in said switch-activating position; and (e) a power source andwireless transmitter connected to said electrical switch, whereuponactivation of said electrical switch transmits power from said powersource to said transmitter, thereby causing a wireless signal to betransmitted to a receiver for activation of an alarm.
 14. The fluid flowswitch and alarm apparatus of claim 13, wherein said electrical switch,power source and wireless transmitter are connected with said housing asa single integrated unit.
 15. The fluid flow switch and alarm apparatusof claim 14, wherein said transmitter includes an antenna connectedthrough said housing to a metallic gas-operated appliance and/ormetallic gas source, thereby converting said metallic gas-operatedappliance and/or metallic gas source to an extended antenna.
 16. Thefluid flow switch and alarm apparatus of claim 13, including a timermechanism for delaying activation of said alarm for a predeterminedperiod of time after said electrical switch is activated in response todetecting the presence of fluid flowing through said piston chamber. 17.The fluid flow switch and alarm apparatus of claim 16, wherein saidinlet port of said housing is connected in-line with a gas source, andsaid outlet port of said housing is connected in-line with agas-operated appliance, said gas-operated appliance including anactivity sensor and means for resetting said timer upon detectingoperator use of said gas-operated appliance.
 18. The fluid flow switchand alarm apparatus of claim 17, wherein said receiver and said alarmare mounted either on said gas-operated appliance, remotely of saidgas-operated appliance, or both.
 19. The fluid flow switch and alarmapparatus of claim 17, wherein said gas-operated appliance carries atransmitter that is electrically triggered by said activity sensor totransmit a wireless signal to a remote receiver for resetting a delaytimer associated with a remote alarm.
 20. A fluid flow switch fordetecting exceptionally low rates of fluid flow, comprising: (a) aswitch housing with an inlet port, an outlet port elevated relative tosaid inlet port, and an interior chamber extending between andcommunicating with said inlet port and said outlet port; (b) a pistoncylinder coaxially disposed within said chamber of said housing, saidpiston cylinder having a cylinder wall with a fluid-flow orificecommunicating with said chamber, and having opposite ends adjacent saidinlet and said outlet ports, said end adjacent said inlet port beingopen and said end adjacent said outlet port being capped to direct theflow of fluid through said fluid-flow orifice in said cylinder wall; (c)a gravity-induced piston carried within said piston cylinder, saidpiston being movable from a lower resting position to an elevatedswitch-activating position in response to the presence of fluid flowingthrough said piston cylinder, and being returned to said restingposition under the force of gravity in the absence of fluid flowingthrough said cylinder; (d) an electrical switch operatively disposed foractivation upon movement of said piston to said switch-activatingposition; and (e) a piston biasing member being disposed adjacent saidcapped end of said piston cylinder and being adapted to impose anonlinear attractive force on said piston which counters the force ofgravity and increases as said piston draws closer to said biasingmember.